wm8742 Wolfson Microelectronics plc, wm8742 Datasheet - Page 21

• Manufacturer Part Number: wm8742
• Description: 24-bit 192khz Dac With Advanced Digital Filtering
• Manufacturer: Wolfson Microelectronics plc

Production Data
DIGITAL AUDIO INTERFACE
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2-WIRE SERIAL CONTROL MODE
The WM8742 supports software control via a 2-wire serial bus. Many devices can be controlled by
the same bus, and each device has a unique 7-bit address (this is not the same as the 7-bit address
of each register in the WM8742).
The WM8742 operates as a slave device on the 2-wire control bus. The controller indicates the start
of data transfer with a high to low transition on SDIN while SCLK remains high. This indicates that a
device address and data will follow. All devices on the 2-wire bus respond to the start condition and
shift in the next eight bits on SDIN (7-bit address + Read/Write bit, MSB first). If the device address
received matches the address of the WM8742 and the R/W bit is ‘0’, indicating a write, then the
WM8742 responds by pulling SDIN low on the next clock pulse (ACK).
recognised or the R/W bit is ‘1’, the WM8742 returns to the idle condition and wait for a new start
condition and valid address.
Once the WM8742 has acknowledged a correct address, the controller sends the first byte of control
data (B15 to B8, i.e. the WM8742 register address plus the first bit of register data). The WM8742
then acknowledges the first data byte by pulling SDIN low for one clock pulse. The controller then
sends the second byte of control data (B7 to B0, i.e. the remaining 8 bits of register data), and the
WM8742 acknowledges again by pulling SDIN low.
The transfer of data is complete when there is a low to high transition on SDIN while SCLK is high.
After receiving a complete address and data sequence the WM8742 returns to the idle state and
waits for another start condition. If a start or stop condition is detected out of sequence at any point
during data transfer (i.e. SDIN changes while SCLK is high), the device reverts to the idle condition.
Figure 13 2-wire Serial Control Interface
The WM8742 device address can be configured between two options.
SADDR pin.
Table 10 2-wire Serial Control Mode Address Selection
PCM MODE
There are a number of valid PCM data input modes. Two channel and one channel differential mono
modes can be selected by serial or hardware control. It is also possible to bypass the WM8742 digital
filters and apply a signal at a rate 8fs (where fs is the sampling rate) directly to the switched capacitor
stage.
PIN
28
SADDR/I
NAME
CSB/
2
S
0 = 2-wire address 0011010
1 = 2-wire address 0011011
DESCRIPTION
PD, Rev 4.2, August 2009
This is selected by the
If the address is not
WM8742
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